Stabilized maleic anhydride



States Unite This application relates to a specification grade solidmaleic anhydride product in dust-free, particulate form containing asmall amount of flaking agent, and also to processes for converting sucha material from the liquid form to the particulate solid form byflaking, and more particularly it relates to such a product and processWherein the flaking agent is phthalic anhydride.

Maleic anhydride is a commercially important material and for manypurposes it is packaged and shipped in free flowing solid form such asflakes, or the flakes may be converted to briquettes. Specificationgrade maleic anhydride may contain a small amount or trace of maleicacid as well as of xylene or the like azeotroping agent, and suchmaterial tends to form powder or dust when the molten material is flakedin a conventional manner. Such dust is particularly bothersome from themanufacturing viewpoint (requiring costly shut-down for cleaning out),gives rise to health hazards, and also increases losses due toevaporation from the relatively extensive surface thereof. The art isconfronted by the problem of providing substantially dust-freespecification grade maleic anhydride in free-flowing solid orparticulate form, as well as methods for producing such a product in aconvenient and economic manner.

The discoveries associated with the invention and relating to thesolutions of the above problems, and the objects achieved in accordancewith the invention as set forth herein include the provision of:

A specification grade maleic anhydride product in dustfree, solid,particulate form containing phthalic anhydride as a flaking agent, theamount of the flaking agent being insufficient to render the compositionoif-grade and yet sufficient to permit converting the molten material tothe desired form by flaking, without dusting;

A method for producing specification grade maleic anhydride product indust-free, solid particulate form which comprises flaking molten maleicanhydride containing phthalic anhydride as a flaking agent, the amountof the flaking agent being insufficient to render the compositionoif-grade and yet sufficient to permit converting the molten material tothe desired form by flaking, without dusting;

Such a method or product wherein the amount of flaking agent is in therange of 0.07 to 0.1 Weight percent;

Such a method or product wherein the product contains a small amount ofxylene;

Such a method or product wherein the product contains a small amount ofmaleic acid;

Such a method wherein the flaking drum is rotated at a speed of 8 to- 12rotations per minute;

Such a method wherein the molten material is maintained at a temperaturein the range of 53 to 60 C.;

Such a method wherein the cooling medium in the flaking drum is at atemperature in the range of 16 to 28 C.;

And other objects which will be apparent as details or embodiments ofthe invention are set forth hereinafter;

In order to indicate still more fully the nature of the presentinvention, the following examples of typical procedures are set forth inwhich parts and percent mean part and percent by weight, respectively,unless otherwise indicated, it being understood that these examples arepresented as illustrative only and are not intended to limit the scopeof the invention.

The following runs are carried out by converting the atent moltenmaterial into flake form by applying the material in a thin layer to arevolving drum on which the material cools, solidifies, and is removedin flake form by a stationary knife. The apparatus used includes arevolving drum cooled by water which drum dips in a shallow heated panfilled with the molten material. A knife or doctor against the drumremoves the product from the surface in solid form.

The charge of maleic anhydride is brought to a temperature of about 58C. and the cooled rotating drum is brought into the pan. The interior ofthe drum is cooled by means of water at 16 to 28 C. The followingresults are obtained using a 5 in. diameter drum.

Example I High purity maleic anhydride (MP. of about 52.6 C.) is meltedtogether with 0.1 wt. percent thereof of phthalic anhydride and themixture is flaked using a drum speed of 10 rpm. The product obtained isoblong in form with the majority of the particles of inch to: /2 inch inlength about inch in width and about 10- to 13- thousandths of an inchthick. This product is dust-free and does not tend to cake up readily onstanding.

Comparative Example A In a comparative run, except using no additivesmall flakes of about one-fourth or less in size of those of Example Iare obtained, with considerable dust. Upon standing the product tends tocake rather rapidly.

The procedure of the invention gives specification grade product inlarge particulate form which is free-flowing and dust-free, asillustrated in Example I. On the other hand, the comparative run withoutthe additive produces unsatisfactory particles and an undesirable amountof dust.

These runs are repeated with specification grade maleic anhydridecontaining a trace of xylene and comparable results to Example I areobtained with the additive; on the other hand, if no additive is presentmost of the product is in the form of a fine troublesome dust.

The maleic anhydride starting material as well as the product is ofspecification grade, and this grade is defined as:

M.P.: 52.4-52.8 C.

Color (Hazen) 20 or less (for the molten material) 5% xylene solution:Clear Purity: 99.5% minimum The standard used to indicate the quantityor intensity of color of the products in molten or liquid form is knownas the A.P.H.A. standard color test. This test in one developed by theAmerican Public Health Association which is known as the HazenPlatinum-Cobalt Scale a description of which is found on page 2048 ofthe 5th edition of Standard Methods of Chemical Analysis, by Wilford W.Scott.

Comparable results to the foregoing are achieved with variousmodifications thereof, including the following:

The flaking agent may be added as a solid or a liquid, before the meltis flaked.

The flaking may be carried out on large commercial type apparatus whichmay be of a diameter of 3 to 4 feet, and this gives relatively largerflakes, if dust-free material is obtained with the small diameterapparatus.

The amount of flaking agent is insuflicient to render the compositionoff-grade; however, it is sufficient to permit converting the moltenmaterial to the desired form by flaking, without dusting. In the absenceof the flaking agent, the starting material tends to dust and givesparticles of an undesirably small size. The preferred amount of flakingagent is the minimum required to attain the desired flaking effect, andgenerally an amount of 0.07 and 0.1 weight percent is eflective.

The initial or starting maleic anhydride may contain a small amount ofXylene or the like azeotroping agent and it may contain a small amountof maleic acid.

The flaking operation is conducted with the melt at a temperature at arange of about 53 to 60 C., preferably about 55 to 58 C. The coolingmedium in the flaking drum may be a temperature in the range of 16 to 28C. The flaking drum is preferably rotated at a speed of 8 to 12rotations per minute for the small drum. Higher speeds give too smalland thin particles, and lower speeds give too small particles.

The results achieved in accordance with the invention are indeedsurprising, especially in view of the many materials tested and foundunsatisfactory.

In view of the foregoing disclosures, variations and modificationsthereof Will be apparent to one skilled in the art and it is intended toinclude Within the invention all such variations and modificationsexcept as do not come within the scope of the appended claims.

What is claimed is:

1. A substantially dust-free flaked composition consisting essentiallyof at least 99.5 Wt. percent maleic anhydride and at least 0.07 wt.percent phthalic anhydride.

2. A product of claim 1 wherein the amount of flaking agent is in therange of 0.07 to 0.1 Weight percent.

3. A product of claim 1 wherein the product contains a small amount ofXylene.

4. A product of claim 1 wherein the product contains a small amount ofmaleic acid.

References Cited in the file of this patent UNITED STATES PATENTS2,770,630 Miller Nov. 13, 1956 OTHER REFERENCES Riegel: IndustrialChemistry (Fifth Edition, 1949), page 876, TP 145, R54.

1. A SUBSTANTIALLY DUST-FREE FLAKED COMPOSITION CONSISTING ESSENTIALLYOF AT LEAST 99.5 WT. PERCENT MALEIC ANHYDRIDE AND AT LEAST 0.07 WT.PERCENT PHTHALIC ANHYDRIDE.